In this specification, abbreviated names of halogenated hydrocarbon compounds are described in brackets after the compound names, and in this specification, the abbreviated names are employed instead of the compound names as the case requires.
Heretofore, as a working fluid for heat cycle such as a refrigerant for a refrigerator, a refrigerant for an air-conditioning apparatus, a working fluid for power generation system (such as exhaust heat recovery power generation), a working fluid for a latent heat transport apparatus (such as a heat pipe) or a secondary cooling fluid, a chlorofluorocarbon (CFC) such as chlorotrifluoromethane or dichlorodifluoromethane or a hydrochlorofluorocarbon (HCFC) such as chlorodifluoromethane has been used. However, influences of CFCs and HCFCs over the ozone layer in the stratosphere have been pointed out, and their use is regulated at present.
Under the above conditions, as a working fluid for heat cycle, a hydrofluorocarbon (HFC) which has less influence over the ozone layer, such as difluoromethane (HFC-32), tetrafluoroethane or pentafluoroethane (HFC-125) has been used, instead of CFCs and HCFCs. For example, R410A (a pseudoazeotropic mixture refrigerant of HFC-32 and HFC-125 in a mass ratio of 1:1) is a refrigerant which has been widely used. However, it is pointed out that HFCs may cause global warming.
R410A has been widely used for a common air-conditioning apparatus such as a so-called package air-conditioner or room air-conditioner, due to its high refrigerating capacity. However, it has a global warming potential (GWP) of so high as 2,088, and accordingly development of a working fluid with low GWP has been desired. Further, development of a working fluid has been desired on the condition that R410A is simply replaced and existing apparatus will be used as they are.
In recent years, a hydrofluoroolefin (HFO) i.e. a HFC having a carbon-carbon double bond is expected, which is a working fluid having less influence over the ozone layer and having less influence over global warming, since the carbon-carbon double bond is likely to be decomposed by OH radicals in the air. In this specification, a saturated HFC will be referred to as a HFC and distinguished from a HFO unless otherwise specified. Further, a HFC may be referred to as a saturated hydrofluorocarbon in some cases.
2,3,3,3-Tetrafluoropropene (HFO-1234yf) is known as a working fluid having a low global warming potential (GWP). However, although HFO-1234yf has a high coefficient of performance, its refrigerating capacity is low as compared with R410A, and it cannot be used for conventional air-conditioning apparatus, etc., for which R410A has been used, such as a so-called package air-conditioner and room air-conditioner.
As a working fluid employing a HFO, for example, Patent Document 1 discloses a technique relating to a working fluid using trifluoroethylene (HFO-1123) which has the above properties and with which excellent cycle performance will be obtained. Patent Document 1 also discloses an attempt to obtain a working fluid comprising HFO-1123 and various HFCs in combination for the purpose of increasing the flame retardancy, cycle performance, etc. of the working fluid.
It has been know that HFO-1134yf is useful as a HFO to be used for a working fluid for heat cycle, and a technique relating to HFO-1234yf has been developed. For example, Patent Document 2 discloses compositions containing HFO-1234yf obtainable in production of HFO-1234yf by a specific process. There are many compositions disclosed in Patent Document 2, and compositions containing HFO-1234yf and HFO-1123 are included. However, HFO-1123 is disclosed only as a by-product of HFO-1234yf together with many other compounds, and Patent Document 2 failed to disclose use of a composition containing the two in a specific proportion as a working fluid and that the composition has excellent coefficient of performance and refrigerating capacity.
Heretofore, a combination of HFO-1234yf and HFO-1123 has not been found or indicated in any documents yet, with a view to obtaining a working fluid which is practically useful comprehensively considering the balance of the capacity, the efficiency and the temperature glide as an alternative to R410A.
HFO-1123 is known to undergo so-called self-decomposition at high temperature or with an ignition source under high pressure. Therefore, an attempt to suppress self-decomposition reaction by mixing HFO-1123 with another component such as vinylidene fluoride to form a mixture having a lowered content of HFO-1123 has been reported (Non-Patent Document 1).
However, Non-Patent Document 1 failed to disclose a composition with which a working fluid can be used with durability while maintaining cycle performance of HFO-1123 without any special measures, under the temperature and pressure conditions under which HFO-1123 is used as the working fluid, and a method for stably producing it. In a case where HFO-1123 is used as a working fluid, a composition with which the working fluid does not undergo self-decomposition and a stable production method are necessary.